Disposable articles

ABSTRACT

Improved disposable absorbent articles, such as diapers, catamenial devices and sanitary napkins, are provided which contain certain stabilized insoluble hydrophilic poly(ethylene oxide) polymers as an absorbing media. The polymers are stabilized with a stabilizing amount of poly(ethylene imine).

United States Patent Assarsson [4 1 May 23, 1972 [5 DISPOSABLE ARTICLES[56] References Cited [72] Inventor: Per Gunnar ASS8I'SSOII, Montclair,NJ. FOREGN PATENTS OR APPLICATIONS [73] Assigneei Union CarbideCorporation, New York 1,163,842 9/1969 Great Britain ..260/823 6,613,6093/1967 Netherlands ..260/823 [221 1969 Primary Examiner-Samuel H. Blech2 APPLNQ; 3 4,193 Attorney-Paul A. Rose, Gerald R. OBrien and William R.

Moran [52] U.S. Cl ..128/284, 128/285, 128/290,

128/296, 204/159.14, 260/2 EN, 260/9 R, 260/29.2 [57] ABS CT EP, 260/823 Improved disposable absorbent articles, such as diapers, 1 f g A61f1 A611r 18 catamenial devices and sanitary napkins, are provided which[58] Field of Search ..260/823; 128/287, 290, 285, contain certainstabilized insoluble hydrophilic poly(ethylene oxide) polymers as anabsorbing media. The polymers are stabilized with a stabilizing amountof poly( ethylene imine).

14 Claims, No Drawings DISPOSABLE ARTICLES This invention relates, ingeneral, to improved disposable absorbent articles. In one aspect, thisinvention relates to absorbent articles containing stabilized waterinsoluble hydrophilic poly( ethylene oxide) polymers. In a furtheraspect, this invention relates to disposable absorbent articles such asdiapers, catamenial devices, sanitary napkins, dental rolls, surgicalsponges, obstetrical napkins, incontinent pads and the like. In anotheraspect, this invention relates to the stabilized water insolublehydrophilic poly(ethylene oxide) polymers.

Although disposable absorbent articles for the absorption of body fluidshave been in use for many years they have not always been completelysatisfactory to the user. Numerous materials, variations inconstruction, and absorbents have all been reported in the literature.However, many products currently on the market suffer from thedisadvantage of having poor or inferior absorption properties. In thepast, the usual method employed to increase absorption characteristicswas to add inexpensive materials which had high absorptive capacity suchas fluffed wood pulp and the like, contained between layers of moisturepermeable fabrics. While satisfactory as absorbents for fluids, in manyinstances the article would be bulky and not comfortable. For example,diapers must have a minimum thickness to insure sufficient absorption ofbody fluids. If, however, the material has low absorbing ability, to beacceptable, the diaper would undoubtedly be bulky and not conformproperly to body contours.

Moreover, one of the major disadvantages of the products commerciallyavailable today, is that while they may have relatively high absorptivecapacities, the absorbing media, if subjected to pressure, can release aportion of the absorbed liquid. This is due to the fact that the liquidis physically entrapped within a fibrous structure and a relative slightpressure is all that is needed to cause the liquid to separate from theab sorbent media. This, of course, is highly undesirable, particularlyin catamenial devices.

In U.S. Pat. No. 2,849,000 there is disclosed an improved catemenialdevice wherein the absorbent cotton fibers are coated with a retentionagent to increase absorbency Typical retention agents set forth aresorbitol, mannitol, glycerine, glycols and glycol polymers. Thesecompositions are applied by spraying onto the cotton or by including inthe final washing step when the absorbent cotton bats are manufactured.However, the compositions disclosed while possessing absorbentcharacteristics are soluble and hence can be extracted from the cottonfibers by body fluids.

More recently, it has been found that insoluble hydrophilicpoly(ethylene oxide) polymers are particularly useful in disposableabsorbent articles since they can absorb relatively large amounts ofliquids and retain them even when subjected to pressure. Although thesepolymers are relatively stable over extended periods of time in thepresence of oxygen at temperatures up to about 25 C., at elevatedtemperatures, such as at about 40 C., the polymers degrade in thepresence of small amounts of oxygen. For instance, after less than about6 weeks of storage at 40 C. in water containing only dissolved oxygen,the unstabilized polymer becomes 100 percent water-soluble. (Thewater-solubility of the polymer, which is initially insoluble, is oneuseful indication of the degree of degradation.)

The water-soluble poly(ethylene oxide) polymers, which are used asprecursors in the preparation of the water-insoluble hydrophilicpoly(ethyelene oxide) polymers, also suffer from oxidative degradation.Many stabilizers have been proposed for the soluble polymer. Despite thestructural relationship between the soluble polymers and the subjectinsolu- It is therefore an object of this invention to providedisposable absorbent articles wherein many of the previous disadvantagesare eliminated or greatly reduced. It is a further object of thisinvention to provide an improved disposable absorbent article containinga stabilized insoluble hydrophilic poly(ethylene oxide) polymer as anabsorbing media. Another object of this invention is to provide adisposable absorbent article having improved absorption properties. Afurther object is to provide an absorbent article containing astabilized insoluble hydrophilic polymer comprised of cross-linkedpoly(alkylene oxide). A still further object is to provide an absorbentarticle containing stabilized cross-linked poly(ethylene oxide). Anotherobject is to provide stabilized cross-linked poly(ethylene oxide).Another object of this invention is to provide an improved disposableabsorbent article wherein the polymer is essentially insoluble in bodyfluids. These and other object will readily become apparent to thoseskilled in the art in the light of the teachings herein set forth.

In its broad aspect, the present invention is directed to improveddisposable absorbent articles. The improvement comprises incorporatingin the article a water-insoluble hydrophilic poly(ethylene oxide)polymer which has been stabilized with poly( ethylene imine).

Poly(ethylene oxide) polymers which have been insoluble by cross-linkingare particularly useful because of their ability to incorporate verylarge amounts of liquid, e.g., water, in the order of 25 to times theirdry weight. Moreover, these polymers, in addition to possessing theability to incorporate large amounts of water, are insoluble in waterirrespective of temperature, will retain liquids, solutions andsuspensions and will form gel-like products.

The non-stabilized water-insoluble hydrophilic poly(ethylene oxide)polymers are known compositions. For instance, the nature andpreparation of these insoluble polymers is disclosed in U.S. Pat. No.3,264,202, issued Aug. 2, 1966, to Paul A. King, the disclosure of whichis incorporated herein by reference. The insoluble polymers are preparedby subjecting water-soluble poly(ethylene oxide) polymers to ionizingradiation in a dose sufficient to cross-link the polymer to form therebya water-insoluble polymer. The water-soluble poly(ethylene oxide)polymers that are used to produce the water-insoluble polymers are alsowell known compositions. For instance, their nature and preparation aredisclosed in U.S. Pat. Nos. 3,127,371; 3,214,387; 3,275,998; 3,398,199;and, 3,399,149.

The water-soluble poly(ethylene oxide) polymers are homopolymers ofethylene oxide and copolymers of ethylene oxide with one or more otheralkylene oxides, such as propylene oxide, 1,2-butylene oxide,2,3butylene oxide, isobutylene oxide, styrene oxide, and the like. Thepolymer contains polymerized ethylene oxide in an amount sufficient toimpart water-solubility to the polymer. Thus the minimum proportion ofpolymerized ethylene oxide in the polymer will vary somewhat, dependingupon the nature of the comonomer(s), but in general will be at leastabout 50 weight percent of ethylene oxide, and is preferably at leastabout 75 weight percent of polymerized ethylene oxide. Ethylene oxidehomopolymer is the preferred poly(ethylene oxide) polymer.

The water-soluble poly(ethylene oxide) polymers will usually havemolecular weights such that the reduced viscosity of the polymer will bewithin the range of from about 0.5 to about 75, and higher, andpreferably from about 1 to about 60, or an aqueous viscosity at 25 C. offrom about 225 centipoises measured at a 5 weight percent concentration,to about 12,000 centipoises, and higher measured at a 1 weight percentconcentration.

The reduced viscosity is measured by the following method. Transfer 100ml of acetonitrile to an 8 02., round screw-cap bottle. With constantstirring, introduce into the bottle 0.200 gram of the polymer weighed tothe nearest milligram. Line the screw cap of the bottle with a piece ofaluminum foil, carefully place the cap on the bottle, and tightensecurely. Place the bottle on a suitable can roller with 6-inch (I.D.)roller and allow it to roll for 16:0.5 hours. Remove the bottle from theroller and filter the solution by pressure through a coarse sinteredglass filter. Determine the time in seconds required for the samplesolution to pass through a calibrated Ubbelohde suspended-levelviscometer at 30i0l C. Use a suitable stopwatch with a lO-second dialgraduated in 0.1 second units, ac curate to within 0. l percent whentested over a 60-minute period. Record the time required. Determine andrecord the time in seconds required for the acetonitrile to pass throughthe viscometer. Calculation:

AS- (E/AS) =AC F viscometer correction AS seconds, required foracetonitrile AC seconds, corrected, required for the acetonitrile SSseconds, required for the polymer solution SC seconds, corrected,required for solution S V= specific viscosity R V= reduced viscosity Kconcentration, gm sample per 100 ml acetonitrile For illustrativepurposes, the following table illustrates the relation between theaverage molecular weight of poly( ethylene oxide) homopolymer, reducedviscosity and bulk viscosity of solutions thereof.

wt.% polymer in reduced approx, avg. bulk viscosity aqueacetonitrileviscosity mol. wt. ous soln, at 25 C.

0.2 1.5 150,000 200 cps (wt.% Soln) 0.2 60 10,000,000 7000-9000 cps(lwt.

The water-insoluble hydrophilic poly(ethylene oxide) polymers areproduced by subjecting the above-described water-soluble poly( ethyleneoxide) polymers to sufficient ionizing radiation to cross-link andinsolubilize the polymer, forming thereby a water-insoluble hydrophilicpolymer. As used herein, the term ionizing radiation" includes thatradiation which has sufficient energy to cause electronic excitationand/or ionization in the polymer molecules (where a solvent is employed)but which does not have sufficient energy to affect the nuclei of theconstituent atoms. Convenient sources of suitable ionizing radiation aregamma ray-producing radioactive isotopes such as Co and Cs, spentnuclear fuel elements, X-rays such as those produced by conventionalX-ray machines, and electrons produced by such means as Van de Graaffaccelerators, linear electron accelerators, resonance transformers, andthe like. Suitable ionizing radiation for use in the present inventionwill generally have an energy level in the range from about 0.05 MeV toabout MeV.

The irradiation of the non-crosslinked (water soluble) polymers can becarried out in the solid phase or in solution. Solid polymers can beirradiated in the air, in a vacuum, or under various gaseousatmospheres, while irradiation in solution can be carried with thepolymer dissolved in water, or in mixtures of water and water-miscibleorganic solvents. Any conventional method can be used to bring the solidpolymer or polymer solution into contact with the ionizing radiation.Suitable methods are well known and understood by those skilled in theart.

The exact amount of ionizing radiation to which the polymer must besubjected depends on a number of variables. In general, when irradiationis carried out at relatively low rates and in the presence of freeradical scavengers such as oxygen, extremely high total doses arerequired to produce the water-insoluble hydrophilic polymers. On theother hand, when the irradiation is carried out under conditions whichfavor the relatively long existence of the free radicals produced, forexample, when the irradiation is carried out with a high dose rate, inthe absence of oxygen, or in solution where oxygen is rapidly used up,the formation of water-insoluble hydrophilic polymers take placereadily. The preferred method for producing the water-insolublehydrophilic polymers is to carry out the irradiation in an aqueoussolution of the water-soluble polymer while employing ionizing radiationhaving an energy level in the range of about 0.10 MeV. to about 20 MeV.at a total dose of between about 0.05 and 10 megarads.

Thus, the polymeric hydrophilic gels are comprised of polymers of theformula:

which have been cross-linked and wherein R and R are selected from thegroup consisting of hydrogen, alkyl radicals and alkyl-substituted arylradicals, and wherein R -R are selected from the group consisting ofhydrogen, methyl, phenyl and vinyl radicals and n is greater than 1These hydrophilic gels contain at least one of the structural unitsshown below:

wherein R -;-R, are as indicated above.

The terms insoluble or insolubilize" as employed throughout thespecification are utilized herein to refer to the formation of apolymer, a variable portion of which is essentially insoluble in water,depending upon the radiation dose. These polymers can swell and absorbmay times their weight in water because they are also hydrophilic.

As previously indicated, the articles of this invention containwater-insoluble, hydrophilic poly(ethylene oxide) which has beenstabilized with poly( ethylene imine) the poly(ethylene imines) arethose polymers prepared from ethylene imine and which in a major amountcontain the recumng units:

and in a minor amount the recurring un it:

CHz-CHP L CHr-CH In practice, the poly(ethylene imine) stabilizer isemployed in a stabilizing amount. By the term stabilizing amount asemployed throught the specification and claims, is meant that quantityof poly(ethylene imine) which when admixed with the poly(ethylene oxide)will decrease the rate of degradation over that of the unstabilizedpolymer. it has been observed that as little as about 0.01 weightpercent based on the solid poly(ethylene oxide) polymer, willeffectively stabilize the polymer against degradation. For most purposesa concentration of stabilizer in the range of from about 0.2 to about3.0 weight percent is preferred. However, if desired, concentrations ofpoly(ethylene imine) as high as 50 weight percent can be employed.

The stabilization of the water insoluble, hydrophilic poly(ethyleneoxide) can be effected at various stages in its preparation. Forexample, the poly(ethylene imine) can be added to an aqueous solution ofthe poly( ethylene oxide) and the resulting solution cast into a filmand subsequently crosslinked. The addition of the stabilizer to thepoly)ethylene oxide) solution also imparts a stabilization effect to thesolution itself. Alternatively, the pure solid polymer can be mixed withthe stabilizer and the resulting product extruded or calendered into afilm or other shaped object. The resulting film or object is thencross-linked by irradiation. The addition of the stabilizer beforeextrusion or calendering, imparts a stabilizing effeet while the polymeris melt blended at elevated temperatures. Finally, the water insoluble,hydrophilic poly(ethylene oxide) can be stabilized after the irradiationstep by absorption of the stabilizer from solution.

The stabilized hydrophilic poly(ethylene oxide) polymers can be readilyincorporated into any of the known or commercially available disposablearticles where they are particularly useful for increasing absorbancy.For example, the polymers can be incorporated into diapers of the typedisclosed in US. Pat. Nos. 2,788,003; 2,849,000; 2,860,637; 3,306,293;and 2,667,168. Similarly, they can be incorporated into tampons orsanitary napkins of the type disclosed in U.S. Pat. Nos. 3,121,427;3.070,095 and the like. The polymers can be employed in a wide varietyof ways, such as, for example, as a powder dispersed in and bonded to acellulosic or similar substrate, or as a film of the cross-linkedpolymer sandwiched between layers of the supporting structure. Any ofseveral known methods can be employed to affix the film or powderedpolymer to the substrate.

In general, the amount of hydrophilic gel employed will be dependentupon the particular absorbent article and its intended use. In practice,it has been observed that disposable absorbent articles can be preparedcontaining from about 2 to about 98 weight percent.

The examples below illustrate the efficacy of the stabilizer of theinvention in enhancing the stability of insoluble, hydrophilicpoly(ethylene oxide) polymers.

' ln Examples 1-3, the insoluble hydrophilic poly (ethylene oxide)polymer was prepared by subjecting an aqueous solution containing 4weight percent coagulant grade poly(ethylene oxide) homopolymer having areduced viscosity of about 60 to ionizing radiation having an energylevel of 1 million electron volts to a total dose of about 1 megarad.The ionizing radiation was produced by a Van de Graaff accelerator.

The polymer was produced in the form of a 3-inch wide tape weighing 1gram per linear foot, which had a thin open structured gauze support.The tapes were not dried and were subjected to the following standardprocedure for evaluation in the gel form.

Two pieces of the above-described tape, each 1 foot long, were placed ina jar containing the below-indicated concentration of stabilizer inaqueous solution. The solution was prepared by dissolving an appropriateamount of poly(ethylene imine) in 500 milliliters of distilled water.The jar was loosely covered and then placed in an air oven held at 40 C.A periodic check of the polymer integrity was made by feeling thefirmness of the tape. Also, the pH of the solution plus the polymer wasmeasured periodically, since degradation is usually accompanied by alowering of the pH. The ratings of the tape appearance were as follows:

(+) tape firm, no noticeable degradation (2) tape cohesive, noticeabledegradation due to softness or stringy surface. tape percent destroyed(i.e., 100 percent soluble in water) The stabilizers used, theirconcentrations, and the results of the evaluations are set forth in thefollowing examples.

EXAMPLE 1 In this example a tape was prepared in accordance with theforegoing procedure but without the poly( ethylene imine) stabilizer andserved as a control for comparison purposes. When subjected to the abovestandard procedure the following results were obtained.

TABLE 1 Interval Tape Appearance pH V4 month 3.5

EXAMPLE 2 In this example, a poly(ethylene imine) solution was preparedby dissolving 0.215 gram of poly(ethylene imine) (approximately 50,000molecular weight) in 500 milliliters of water to yield a l0' molarsolution of poly(ethylene imine) monomer units. In this solution wereplaced the tapes in accordance with the standard procedure. Thefollowing results were obtained.

lnterval Tape Appearance pH 34 month 9.4

1% months 8.9

3% months 8.4

6 months 8.8

EXAMPLE 3 A poly(ethylene imine) solution was prepared by dissolving0.0002 gram of poly(ethylene imine) (approximately 50,000 molecularweight) in 500 milliliters of water to yield lO mol ar. In this solutionwere placed the tapes in accordance with the standard procedure. Thefollowing results were obtained.

TABLE 3 Interval Tape Appearance pH month 7.4 1% months 7.4 3%months 7.36 months 8.4

EXAMPLE 4 This example illustrates the stabilization of the hydrophilicpoly(ethylene oxide) by addition of the stabilizer to the aqueouspoly(ethylene oxide) solution prior to cross-linking. The poly(ethyleneimine) has a stabilizing effect on the poly (ethylene oxide) solutionprior to as well as after cross-linking.

Three aqueous solution mixtures were made up containing the followingproportions; (A) 4 weight percent of poly(ethylene oxide) homopolymer'(having a reduced viscosity of about 60) and 0.13 weight percentpoly(ethylene imine) homopolymer (having a molecular weight of about50,000) yielding a solution with a monomer mole ratio of 30:1respectively, (B) 4 weight percent of poly(ethylene oxide) homopolymer(as above) and 0.04 weight percent poly(ethylene imine) homopolymer (asabove) yielding a solution with a monomer mole ratio of 100:1respectively, (C) 4 weight percent of poly(ethylene oxide) homopolymer(as above) and 0.027 weight percent poly(ethylene imine) homopolymer (asabove) yielding a solution with a monomer mole ratio of :1.

These solutions were cross-linked with ionized radiation having anenergy level of one million electron volts to a total dose of about onemegarad. The ionized radiation was produced by a Van de Graaffaccelerator. The polymer gels produced by this process were a 3-inchwide tape weighing about 15 grams per linear foot. The tape had an openstructured gauze support. The tape was dried into a film by exposure toair at room temperature for a period of about 16 hours (overnight). Inthe control experiments wherein no poly(ethylene imine) was added, thetape was produced and dried in a similar manner.

This example demonstrates the efficacy of the added poly(ethylene imine)in three different proportions to stabilize the dried hydrophilicinsoluble poly(ethylene oxide).

One-half foot samples of both stabilized and unstabilized tape werewrapped into a 7.5 inch X 3 inch cotton strip, taped together as a roll,and then placed into an air oven held at 90 C. After varying lengths oftime, the rolls were taken out of the oven, the tape recovered andplaced in 500 milliliters of 10 weight percent water in methanol toextract the degraded soluble polymer. Table IV below depicts the weightof the tape (excluding the gauze) immediately after drying, the weightsof the tape after exposure to the 90 C. air oven for varying lengths oftime followed by extraction, and the weight percent of polymer that wasdegraded after such exposure.

TABLE IV Length of Weight-Grams Time in Before After Percent SampleOven-Hours Oven Oven Degraded Poly(ethylene oxide) Film Not StabilizedNo. l 1 0.7735 0.7064 17.9 2 1.5 0.9574 0.7702 32.7 3 2.5 0.8919 0.667846.1 4 3 0.9448 0.6037 63.6 5 4 0.6891 100 Poly( ethylene oxide) FilmStabilized; Solution (A) 30:1

Poly(ethylene oxide) Film Stabilized, Solution (B), 100:1

Poly( ethylene oxide) Film Stabilized, Solution (C), 150:1

. tion of molecular weight degradation.

TABLE V.VISCOSITY 1N CEN'IIPOISE OF IOLY(ETIIYLENE OXIDE) SOLUTIONS Timein days Smnnle 1 2 5 22 78 106 t ontrnl. 54,000 10,000 50Sluhillzmlsolutions. 50,000 52,000 57,000 01,000 40,000 28,000

EXAMPLE 5 Another method for preparing hydrophilic poly( ethylene oxide)films for use in the disposable articles of this invention, is to meltblend, extrude or calender solid poly(ethylene oxide). Thereafter, theresulting film is cross-linked by irradication. However, degradation isknown to occur during the melt blending and shearing step when thepolymer is at elevated temperatures. This example illustrates thestabilizing effect when poly(ethylene imine) is admixed with the solidpoly(ethylene oxide) prior to blending.

Brabender curves were obtained on solid poly( ethylene oxide) having amolecular weight of about 600,000, using a one half size No. 6 rollerhind with a jacket temperature of C. The charge size selected was 26grams.

The procedure consisted of charging the mixer head at 40 rpm through thequick load chute and with the read out instrument on the 5X scale. Threeminutes later the scale was set at 1X with a 500 m-gm. preloading. Atthe same time, the speed was increased to 100 rpm and the curve wasplotted until the torque level decayed to 75 percent of its originallevel. The time to reach this point was then taken as a measure of thestabilizing efficiency of the stabilizer. This time was measured fromthe point where the speed was increased to 100 rpm, the original torquelevel was also taken at this point. These results are summarized belowin Table VI.

The rate of torque decay was also calculated by using the instananeousslope to the curve at the point where 75 percent of the original torquewas achieved. These results are shown in Table VII.

TABLE VII Sample Percent Rate of Torque No. Stabilizer Decay m-gmJmin.

These data show that 0.25 percent added poly(ethylene imine) has slowedthe rate of decay to one-half that of unstabilized poly( ethyleneoxide).

in sample 1, the melt temperature increased to a maximum of 169 C. atabout 7.5 minutes (measured from the start of the experiment) and thendecayed very rapidly as degradation occurred until at 15-16 minutes ithad equilibrated to the bowl temperature. Sample 2 reached a maximum ofC. at about 14 minutes and then decreased by only 1 C. over the next 14minutes of processing. Sample 3 reached a maximum of 174 C. at about 9minutes and then started to drop very gradually. Sample 4 behaved verymuch like sample 3.

EXAMPLE 6 A set of tampons were made on an in-line production machine byfeeding a l-yard long and 3-inch wide composite strip made byalternately layering two pieces of dried polymer, prepared as in Example4, with a thin gauze support made from solution cocross-linkingpoly(ethylene oxide) with poly(ethylene imine) at a monomer ratio of30:1 respectively and the polymer weighing 4.7 g/yd between three piecesof cotton weighing l2g/yd herein called 2-ply tampons. In a similarmanner tampons with only one piece of the polymer and layered betweenthree pieces of same cotton produced as samples herein called l-plytampons. Control tampons were made by layering four pieces of samecotton weighing 12 g/yd.

The absorption efficiency of these differently constructed tampons weretested in three different apparatus using as absorbing fluid water,physiological saline water, and citrated blood.

1. Apparatus I was constructed by filling a 3-inch diameter plasticbottle about inches deep with a percent poly(ethylene solution),coagulant grade, with a 10 mm glass rod 4 1% inches long imbeded in thecenter and irradiating the bottle and contents in a cobalt 60 source toa total dose of about 1 megarad. The resulting gel with container andwith the rod removed was tilted at a 40 angle with the mouth of the holedownward and connected to a 50 cc burette via a plastic tube goingthrough the backside of the gel to the center hole. Test tampons wereinserted completely through the mouth of the hole and the fluid, in thiscase water, from the burette al lowed to flow into the hole at acontrolled rate of about 10-20 cc/hr. As the tampon became saturated atthe particular pressure in the test apparatus the break-through fluidwas collected and measured, while the tampon was weighed prior to thetest and saturated at the end of the test. Apparatus II was constructedby filling a 3-inch diameter plastic bottle about 5 inches deep with a10 percent poly(ethylene solution), coagulant grade, with a 7 mm glassrod 4 )2 inches long imbeded in the center and irradiating the bottleand contents in a cobalt 60 source to a total dose of about I megarad.The resulting gel with container and with the rod removed was tilted ata 40 angle with the mouth of the hole downward and connected to a 50 ccburette via a plastic tube going through the backside of the gel to thecenter hole. Test tampons were inserted completely through the mouth ofthe hole and the fluid in this case, physiological saline water, fromthe burette allowed to flow into the hole at a controlled rate of aboutl0-22 cc/hr. As the tampon became saturated at the particular pressurein the test apparatus the break-through fluid was collected andmeasured, while the tampon was weighed prior to the test and saturatedat the end of the test.

The absorption capacity results obtained on the test tampons with l-ply(hydrogel with gauze), 2-ply (hydrogel with gauze), and control tamponsare shown in Table VIII below.

TABLE VIII Absorption Studies of Tampons With Stabilized Hydrophilic Invitro conditions at 0.5 pounds per square inch pressure. Monomer moleratio of The absorption capacity results obtained on the test tarnponswith 2 ply film (hydrogel without gauze), 2-ply scrim (hydrogel withgauze) and control tampons are shown in Table IX below.

TABLE IX.-ABSORPTION STUDIES OF TAMPONS WITH STABILIZED HYDROPHILIO POLY(ETHYLENE OXIDE) 1 In vitro conditions at about 1.0 pound per squareinch pressure. Monomer mole ratio of 30:1.

EXAMPLE 7 In addition to tampons, the hydrogels of this invention arealso useful in sanitary napkins. A test mode] was prepared in thefollowing manner. I

' A 10 percent high molecular weight poly(ethylene oxide) solution waspoured into a round open end polyethylene mold 2 k inches in diameterand 5 inches long into which was inserted in the center a glass tube 36inch in diameter to a depth of about Va inch from the back side of themold. This assembly was irradiated in a Cobalt 60 source to a total doseof about l megarad to produce a cohesive but flexible gel. With theglass tube removed and a burette attached through the back of the modelto the center hole, a controlled rate of test fluid (water or salinewater) was delivered through the hole. The model was inclined at about a45 angle using a clamp around the model and with the mouth of the holedownward and the model dressed with a sanitary napkin. Commercialnapkins sold under the trade name Kotex" were sandwiched with two layersof the poly(ethylene oxide)-poly(ethylene imine) film prepared inaccordance with Example 4 (A). The napkins were placed on the modelusing a slow rate of water delivery, about 1 cc per minute. Asignificant improvement on the absorption capacity of the commerciallyavailable napkins with the cross-linked polymer is noted over controlnapkins.

Although the invention has been illustrated bythe preceding examples, itis not to be construed as being limited to the materials employedtherein, but rather, the invention encompasses the generic area ashereinbefore disclosed. Various modifications and embodiments of thisinvention can be made without departing from the spirit and scopethereof.

What is claimed is:

1. In a disposable absorbent article, the improvement which comprisesincorporating in said article at least one hydrophilic polymer of theformula:

which has been cross-linked, wherein R and R, are selected from thegroup consisting of hydrogen, alkyl radicals and alkyl substituted arylradicals, and wherein R R are selected from the group consisting ofhydrogen, methyl, phenyl and vinyl R R Rcoltlelol... i.

radicals, and n is greater than 1, said polymer having incor- 7. Thesanitary napkin of claim 6 wherein said polymer is cross-linkedpoly(ethylene oxide).

8. A tampon containing the stabilized hydrophilic polymer as defined inclaim 1.

9. The tampon of claim 8 wherein said polymer is crosslinked poly(ethylene oxide). 10. A diaper containing the stabilized hydrophilicpolymer as defined in claim 1.

11. The diaper of claim 10 wherein said polymer is crosslinked poly(ethylene oxide).

12. Process for stabilizing water-insoluble hydrophilic

2. The disposable absorbent article of claim 1 wherein said hydrophilicpolymer is comprised of cross-linked poly(alkylene oxide).
 3. Thedisposable absorbent article of claim 1 wherein said hydrophilic polymeris comprised of cross-linked poly(ethylene oxide).
 4. A catamenialdevice containing the stabilized hydrophilic polymer as defined inclaim
 1. 5. The catamenial device of claim 4 wherein said polymer iscross-linked poly(ethylene oxide).
 6. A sanitary napkin containing thestabilized hydrophilic polymer as defined in claim
 1. 7. The sanitarynapkin of claim 6 wherein said polymer is cross-linked poly(ethyleneoxide).
 8. A tampon containing the stabilized hydrophilic polymer asdefined in claim
 1. 9. The tampon of claim 8 wherein said polymer iscross-linked poly(ethylene oxide).
 10. A diaper containing thestabilized hydrophilic polymer as defined in claim
 1. 11. The diaper ofclaim 10 wherein said polymer is cross-linked poly(ethylene oxide). 12.Process for stabilizing water-insoluble hydrophilic poly(ethylene oxide)polymer which comprises incorporating in said polymer at least astabilizing amount of poly(ethylene imine).
 13. The stabilized polymerof claim
 12. 14. Process for stabilizing water insoluble hydrophilicpoly(ethylene oxide) which comprises incorporating in water solublepoly(ethylene oxide) polymer at least a stabilizing amount ofpoly(ethylene imine) and thereafter cross-linking said polymer byexposure to ionizing radiation.